In the (petro)chemical industry or in energy-producing and processing plants, flat gaskets made of rubber-bonded materials and of pressed sheets or pressed films of flexible graphite are often used for flanged joints. The fillers in such cases are mostly fibrous materials, mineral additives, graphite, charcoal, metal or metallic inserts, or appropriate combinations thereof. The fibrous materials can also be specially impregnated.
PTFE has found wide use in flat gaskets requiring very high chemical resistance combined with good sealing and mechanical properties of the gasket material at high temperatures.
It is known from DE-A 44 19 007 to create flat gaskets made of at least one nonwoven fabric prepreg in which a sheeting made of asbestos-free fibers or fiber blends is impregnated with a pre-crosslinkable solution, dispersion or suspension of a reactive polymer mixture, then pre-crosslinked by drying at an elevated temperature and optionally laminated to a plastic or metal film.
Document EP-B 654 625 discloses flat gaskets consisting of microporous, stretched PTFE that are provided at least in part with a solvent-resistant polymeric lacquer.
Document U.S. Pat. No. 5,997,008 describes a sealing ring consisting of a corrugated metallic ring which, at least on one side, is provided with a nonmetallic coating exhibiting a low coefficient of friction, for example with a PTFE coating, and acting as a microsealing layer.